Polystyrene beads are produced by heating an agitated suspension of styrene, having a free-radical-generating initiator dissolved therein, in an aqueous medium with the aid of a suspending agent. The suspending agent may be a finely-divided solid (e.g. tricalcium phosphate or zinc oxide) or a film-forming, water-soluble polymer (e.g. hydroxyethyl cellulose or polyvinyl alcohol). The time-temperature cycle is determined by the rate at which free radicals are generated and consumed to form polymer. The free radicals are created by the influence of heat on the monomer and the initiator. The polymerization of styrene at 90.degree. C. with benzoyl peroxide as primary initiator proceeds at a rate of about 13-15% conversion per hour and yields polymer with a typically broad molecular weight distribution. The polymerization of styrene at 115.degree.-130.degree. C. with t-butyl perbenzoate as primary initiator proceeds at a rate of about 25-35% per hour. However, the molecular weight distribution of the polystyrene made at the higher temperature is narrower although the solution viscosity may be identical with that made at the lower temperature.